Influence of external grounded screens on the electric field structure in a drift chamber

The structure of electric fields in a drift chamber is considered both taking into account the influence of adjacent components and the presence of dielectric walls. It is shown that additional field shaping electrodes can preserve the uniformity of the electric field in the detector and protect it from the distortion by an external grounded screen. This design allows the first drift cell to end as close as 5 mm from the outer surface of the grounded screen. It was incorporated in the FTC detector in the L3 experiment at CERN.